Dunces primarily sent up Hoskins's often blue material? (5)
I believe the answer is:
denim
'blue material?' is the definition.
(I've seen this in another clue)
'dunces primarily sent up hoskins's' is the wordplay.
'primarily' says to take the initial letters.
'sent up' shows that the letters should be reversed in order.
'hoskins's' becomes 'mine' (where the crossword setter is 'Hoskins').
The first letter of 'dunces' is 'd'.
'mine' backwards is 'enim'.
'd'+'enim'='DENIM'
'often' acts as a link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for denim that I've seen before include "Twill cloth" , "Hard-wearing cotton fabric" , "Tough cotton fabric" , "Durable material" , "Fabric used for jeans" .)